Carbon Dots as New Effective Catalysts for Knoevenagel Condensation Reaction and Synthesis of Cyclic Carbonates under Solvent‐free Conditions

Abstract

Carbon dots (CDs) as new efficient catalysts have been developed for the Knoevenagel condensation reaction and the synthesis of cyclic carbonates under solvent‐free conditions. Six kinds of carbon dots with different numbers of amino groups were synthesized. The amine‐terminated carbon dot (NCDs‐1) was synthesized using arginine and ethylenediamine by a microwave technique, and its catalytic action was studied. NCDs‐1 with the highest numbers of amino groups was used as new metal‐free and effective heterogeneous catalysts to perform essential Knoevenagel condensation and cycloaddition reactions in solvent‐free conditions. 1H NMR was used to demonstrate the Knoevenagel condensation mechanism, in situ Fourier infrared spectroscopy was used to investigate CO2 cycloaddition and a catalytic mechanism was postulated. NCDs‐1 showed a yield of 96.3±1.5 % for Knoevenagel condensation of benzaldehyde and malononitrile. In addition, NCDs‐1/TBAB showed a yield of (97.0±1.0 %) of 4‐phenyl‐1,3‐dioxolan‐2‐one for styrene oxide at 100 °C and 0.1 MPa in 1.5 h. A simple and convenient method for catalytic reactions with amine‐terminated carbon dots was developed.